1. Field of the Invention
The present invention relates to a sheet bending apparatus for performing a center-bending processing to a recording sheet to which a predetermined processing has been performed previously by an upstream device such as an image forming apparatus and discharging the same, and a sheet postprocessing apparatus.
2. Description of the Related Art
Generally, in a case where a side end aligning and a obliqueness correction is performed to a recording sheet placed in a sheet holding member by using a pair of side end aligning members, it is preferable that the side end aligning members have a length long enough to cover a substantially entire length of the sheet holding member.
However, since the center-folding apparatus is provided with bending rollers and a bending blade each having a length covering a full width of the sheet holding member and positioned at a central portion thereof, the side end aligning members are likely to be provided respectively on upstream and downstream in a sheet conveyance direction and formed integrally with the side end aligning members on upstream and downstream so as to stride across the bending rollers and the bending blade.
However, the integrally formed side end aligning members include the ones on upstream are supported respectively by the other ones on downstream in a cantilever state. Accordingly, the side end aligning and the obliqueness correction are substantially performed only on downstream. Consequently, an effect of the side end aligning and the obliqueness correction performed on upstream is not considered to be sufficient. The reason is as follows. Namely, after a recording sheet is placed in the sheet holding member, a frictional resistance generated between the recording sheet and the sheet holding member becomes great, and a great force is required to overcome the frictional resistance and to move the recording sheet with the side end aligning members. For example, if such a great force is applied to a recording sheet which is so thin, there is likelihood causing the recording sheet to be deformed.
In this regard, a frictional resistance generated between the recording sheet and the sheet holding member becomes small during when the recording sheet is in course of being conveyed into the sheet holding member. Accordingly, a small force would be enough for overcoming the small frictional resistance and moving the recording sheet in opposite width directions using the side end aligning members. Consequently, if such a small force is applied to a thin recording sheet and the like, the recording sheet would be less likely to be deformed.
Thus, in the side end aligning and the obliqueness correction performed to the recording sheet using the side end aligning members, it is more advantageous to perform the side end aligning and the obliqueness correction by the side end aligning members on upstream with which a recording sheet comes in contact when the recording sheet is in course of being conveyed into the recording sheet holding member rather than performing the same by the side end aligning members on downstream with which a recording sheet comes in contact after the recording sheet is placed in the holding member.
In this regard, the Japanese Unexamined Patent Publication No. 2002-167120, for example, discloses a pair of side end aligning members provided on opposite side ends and positioned only on upstream from a sheet bending member in a sheet conveyance passage.
However, even though it is more advantageous to perform the side end aligning and the obliqueness correction by using the side end aligning members provided on upstream with which a recording sheet comes in contact when the recording sheet is in course of being conveyed into the recording sheet holding member than performing the same by using the side end aligning members provided on downstream with which a recording sheet comes in contact after the recording sheet is placed in the holding member, if the pair of side end aligning members are positioned only on upstream from the sheet bending member as disclosed in the prior art, an effect of the side end aligning and the obliqueness correction on downstream would not be sufficient since the side end aligning and the obliqueness correction are performed only on upstream. Thus, an alignment of side ends of recording sheets at the time of performing the center-folding processing could not be enhanced in this case.